Means for converting acoustic into electric energy



A. MEIS$NER MEANS FOR CONVERTING ACOUSTIC INTO ELECTI KIC ENERGY Oat 24, 1933.

Filed Oct. 29, 1929' INVENTOR ALEXANDER MEISSNER ATTORNEY Patented Oct. 24, 1933 MEANS FOR CONVERTING ACOUSTIC INTO ELECTRIC ENERGY Alexander Meissner, Berlin, Germany, assignor' to Telefunken Gesellschaft fur Drahtloee 'lelegraphic m. b. 11., Berlin, Germany, a corporation of Germany Application October 29, 1929, Serial No. 403,841,

d in Germany November 22. .1928

2 Claims. (01- 179-421) This invention relates to acoustic devices. be of a nature as approximately shown in Fig- More particularly it relates to acoustic devices in which the vibratile diaphragm is ailected by standing waves or air columns.

5 Modern microphones when used for the broadcasting of high class music often exhibit the undesirable property thatat some frequencies, especially relatively high frequencies, .a standing wave is produced above the sound-impactedsurface or funnel shaped air columns are produced whereby the uniform operation -of the instrument is impaired. These disturbances could be likened in some regards to'disturbances or obstacles suffered by a current of air at surfaces (baffles) l5 placed in its path; Figure 1 shows these disturbances associated with an operation of a microphone which had asurface approximatelythree centimeters in diameter. Disturbing actions are clearly discernible at points A, B and C and these are not due to natural vibrations of the microphone diaphragm, but are rather ascribable to the circumstance that standing air columns have been produced at these frequencies above the surface. Possibly also a sort of funnel has been set up above the microphone surface at these frequencies at which the sound is deflected upon both sides (Figure 2) similarly as an air current.

Now, the ways and means here disclosed serve to obviate reflections and eddying upon the surface of the microphone, or these actions are at least diminished to a large degree. The basic idea of the invention is that the surface receiving or impacted by the sound is provided with apertures through which the sound wave passes so that the sound waves act upon the microphone surface without losing its character. If the active microphone surfaces are subdivided in a way as shown in Figure 3 the sound wave passes through the openings a thereof so that no standing waves and disturbances are able to arise,

upon the subdivisional small sized microphone surfaces. Also the disturbances due to eddies in the rear of the microphone surfaces are small if the relation between the useful or active surface b and the section of the openings a is chosen correspondingly. A microphone surface or diaphragm according to this invention would then ure4.

The arrangement can be carried into effect most readily with microphones consisting of artiiicial piezo-electric substances, or of materials which serve as a dlelectricfor a condenser microphone.

The shaded parts b. in the illustration are the active surfaces, whllethe unshaded areas it constitute cavities. In order that all active surfaces may simultanenously act towards the outside, they are inter-connected by metal strips or bridge pieces. Upon the posterior face these microphone surfaces may be stiffened by suitable reinforcing strips as shown in Figure 5.

A technically simple arrangement is obtained by disposing the active microphone surfaces stripfashion adjacent to one another 'as shown in Figure 6. According to another modification wires are covered with active microphone layers, by securing thereon a cooperating electrode and causing the sound to impact upon this wire network.

- In this modification which is illustrated by Figure 7 the optimum relationship between wire diameter and opening (mesh) being selected so as to suit a given frequency range.

In the above arrangement it is advisable to use either plaza-electric substances as the active microphone material in the form of plates, strips or wires. or else-to have recourse to arrangements in which these substances are employed as fillers for the air-gap of .a condenser microphone with or without additional biasing tension.

I claim:

unimpededly.

ALEXANDER MEISSNER. 

